The radiation CT device enables tomogram to be obtained in a shorter time as compared to a case when an MRI or a PET (Positron Emission Tomography) is used. In order to provide a high-definition and high-resolution image by expanding the feature further, a radiation detector having a structure of multi-channel array has been gradually used. In the radiation CT device, a plurality of radiation detectors are placed in an arc shape at opposite side of a radiation source with respect to an object to be photographed. For a single channel array radiation detector, in each radiation detector, eight or sixteen radiation detecting elements are arranged lengthwise or breadth-wise. For a multi-channel array radiation detector, for example, sixty four and sixteen radiation detecting elements are arranged lengthwise and breadth-wise, respectively, in a lattice manner. By replacing a single channel array radiation detector in which radiation detecting elements are arranged in one line with an m multi-channel array radiation detector in which radiation detecting elements are arranged in m lines, inspection time can be shortened, and high-resolution and high-definition tomogram can be provided.
Since in the multi-channel array radiation detector, for example, 1024 radiation detecting elements are arranged in sixteen columns by sixty four rows for a radiation detector, the size of the radiation detecting elements to be used becomes small. Moreover, the gap between neighboring radiation detecting elements becomes small. By the reason, the scintillator element of each radiation detecting element becomes small, resulting in a small gap between neighboring scintillator elements.
In the multi-channel array radiation detector, since individual radiation detecting elements become small, in order to prevent light scintillated by a scintillator element from emitting through the side surfaces of the scintillator element, and prevent the output from lowering, it is necessary to dispose a light-reflecting material having high light-reflectivity to the side surfaces of the scintillator element. Moreover, in order to prevent image broadening because of the fact that radiation that has passed through the neighboring scintillator element comes into another scintillator element, and to provide a high-definition image, it is necessary to provide a radiation shielding material close to the side surfaces of the scintillator element.
As the scintillator element becomes small, the gap between neighboring scintillator elements should be small, and it has been difficult to interpose a radiation shielding plate between light-reflecting materials disposed on the side surfaces of the scintillator element.
In the radiation detector, a radiation shielding plate made of heavy metal element, such as tungsten or lead, is interposed between the scintillator elements to prevent cross-talk. Further, the detection efficiency is enhanced with a light-reflecting material filled in between the scintillator element and the radiation shielding plate, because, among light scintillated by the scintillator element, light that has leaked around the scintillator element returns into the scintillator element.
As the light reflecting material, a resin such as epoxy and polyester blended with white pigment such as titanium oxide powder is usually used, and the light reflecting material has light-reflectivity of around 90%. However, if light scintillated by the scintillator element is emitted from the side surface of the scintillator element into the light-reflecting material, it is attenuated by resin contained in the light-reflecting material. Due to the attenuation, sensitivity of the radiation detector is lowered, thereby, in order to compensate the attenuation, it has been necessary to use white pigment having high light-reflectivity.
Moreover, since the light-reflecting material that is a resin blended with white pigment is pretty thick as at least 100 μm, the radiation shielding plate is apart by the light-reflecting material thickness from the side surface of the scintillator element. Since the radiation shielding plate is apart from the side surface of the scintillator element, sometimes, radiation incident at low angle (a small angle with respect to the side surface of the scintillator element) may be shielded by the radiation shielding plate, but radiation passing only through the light-reflecting material comes into the scintillator element.
If, in order to shield radiation incident at low angle, a radiation shielding plate made of a heavy metal element plate with a thickness near the gap between the scintillator elements is used, the thickness of the light-reflecting material should be thin, thereby, the warping of the radiation shielding plate cannot be absorbed by the light-reflecting material. By the reason, it becomes difficult to assemble the scintillator elements by arranging them lengthwise and breadth-wise in high accuracy through a small gap. The problem becomes notable when, as the multi-channel array radiation detector, the gap width between the scintillator elements is narrow.
It is proposed in Patent Documents 1 to 4 to use resin blended with heavy metal element powder as the radiation shield material, in place of the heavy metal element plate. Consideration to use the resin blended with heavy metal element powder as the radiation shield material filled between the scintillator elements of the radiation detector, has led to the present invention.
Patent Document 1: Japanese Laid-Open Patent Hei 5-264789
Patent Document 2: Japanese Laid-open Patent Hei 8-122492
Patent Document 3: Japanese Laid-open Patent 2002-365393
Patent Document 4: Japanese Laid-open Patent 2003-28986